Warewasher with heat recovery system

ABSTRACT

A warewash machine for washing wares includes a chamber for receiving wares, the chamber having at least one wash zone. A waste heat recovery unit is arranged to transfer heat from exhaust air of the machine to incoming water traveling along a water flow path through the waste heat recovery unit to a booster heater of the machine. A refrigerant medium circuit includes at least a first condenser arranged to deliver refrigerant medium heat to the incoming water. A control arrangement monitors subcooled refrigerant medium condition and responsively modifies operation of one or more of: (i) speed of a compressor of the refrigerant medium circuit, (ii) speed of an exhaust fan that causes air flow across the waste heat recovery unit or (iii) speed of a pump that controls incoming water flow along the water flow path.

TECHNICAL FIELD

This application relates generally to warewashers such as those used incommercial applications such as cafeterias and restaurants and, moreparticularly, to a heat recovery system that adapts to operatingconditions of the warewasher.

BACKGROUND

Commercial warewashers commonly include a housing area which defineswashing and rinsing zones for dishes, pots, pans and other wares. Heatrecovery systems have been used to recover heat from the machine thatwould ordinarily be lost to the machine exhaust.

Waste heat recovery systems such as a heat pump or refrigeration systemuses evaporator(s), compressor(s) and condenser(s) such that theoperation involves thermal fluids (including refrigerant) for recoveringwaste energy and re-using captured energy at areas of interest. Thesystems require the thermal fluid to operate within a specified envelopeto prevent system shut down from high or low pressure, hence, the needfor effective controls.

It would be desirable to provide a heat recovery system that adapts tomachine operating conditions in order to make more effective use of heatrecovery. It would also be desirable to provide a heat recovery systemthat is able to more effectively maintain desired subcooled condition ofrefrigerant medium. It would also be desirable to support such heatrecovery systems to enable operation continuously or semi-continuouslyat startup, at steady state or at the standby or idle mode whilesimultaneously recovering waste energy and tempering the waste hotstream to a predetermined temperature by the use of thermal fluid(s).

SUMMARY

In one aspect, a warewash machine for washing wares includes a chamberfor receiving wares, the chamber having at least one wash zone. A wasteheat recovery unit is arranged to transfer heat from exhaust air of themachine to incoming water traveling along a water flow path through thewaste heat recovery unit to a booster heater of the machine. Arefrigerant medium circuit includes at least a first condenser arrangedto deliver refrigerant medium heat to the incoming water. A controlarrangement monitors subcooled refrigerant medium condition andresponsively modifies operation of one or more of: (i) speed of acompressor of the refrigerant medium circuit, (ii) speed of an exhaustfan the causes air flow across the waste heat recovery unit or (iii)speed of a pump that controls incoming water flow along the water flowpath.

In another aspect, a warewash machine for washing wares includes achamber for receiving wares, the chamber having at least one wash zone.A waste heat recovery unit is arranged to transfer heat from exhaust airof the machine to incoming water traveling along a water flow paththrough the waste heat recovery unit into the machine. A refrigerantmedium circuit includes a condenser arranged to deliver refrigerantmedium heat to the incoming water. A control arrangement includes one ormore sensors and a controller for determining a condition of subcooledrefrigerant medium in the refrigeration medium circuit. The controlleris configured to vary, based at least in part upon the condition of thesubcooled refrigerant medium, one or more of: (i) a speed of acompressor of the refrigerant medium circuit, (ii) a speed of an exhaustfan the causes air flow across the waste heat recovery unit or (iii) aspeed of a pump that controls incoming water flow along the water flowpath.

In a further aspect, a method is provided for adaptively controlling awarewash machine that includes a chamber for receiving wares, thechamber having at least one wash zone, a refrigerant medium circuitincluding at least one condenser through which the incoming water to themachine flows, and a waste heat recovery unit through which incomingwater to the machine flows. The method involves: identifying anunder-condensed condition of subcooled refrigerant medium in therefrigerant medium circuit or an over-condensed condition of subcooledrefrigerant medium in the refrigeration medium circuit; and in responseto identification of the under-condensed or over-condensed condition,varying at least one of (i) a speed of a compressor of the refrigerantmedium circuit, (ii) a speed of an exhaust fan that causes air flowacross the waste heat recovery unit or (iii) a speed of a pump thatcontrols incoming water flow through the waste heat recovery unit andthe condenser.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side elevation of one embodiment of a warewasher;and

FIG. 2 is a schematic depiction of a refrigerant circuit and an incomingwater flow path of the warewash machine.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary conveyor-type warewash machine,generally designated 10, is shown. Warewash machine 10 includes ahousing 11 that can receive racks 12 of soiled wares 14 from an inputside 16. The wares are moved through tunnel-like chambers from the inputside toward a blower dryer unit 18 at an opposite exit end 17 of thewarewash system by a suitable conveyor mechanism 20. Either continuouslyor intermittently moving conveyor mechanisms or combinations thereof maybe used, depending, for example, on the style, model and size of thewarewash system 10. Flight-type conveyors in which racks are not usedare also possible. In the illustrated example, the racks 12 of soiledwares 14 enter the warewash system 10 through a flexible curtain 22 intoa pre-wash chamber or zone 24 where sprays of liquid from upper andlower pre-wash manifolds 26 and 28 above and below the racks,respectively, function to flush heavier soil from the wares. The liquidfor this purpose comes from a tank 30 and is delivered to the manifoldsvia a pump 32 and supply conduit 34. A drain structure 36 provides asingle location where liquid is pumped from the tank 30 using the pump32. Via the same drain structure, liquid can also be drained from thetank and out of the machine via drain path 37, for example, for a tankcleaning operation.

The racks proceed to a next curtain 38 into a main wash chamber or zone40, where the wares are subject to sprays of cleansing wash liquid(e.g., typically water with detergent) from upper and lower washmanifolds 42 and 44 with spray nozzles 47 and 49, respectively, thesesprays being supplied through a supply conduit 46 by a pump 48, whichdraws from a main tank 50. A heater 58, such as an electrical immersionheater provided with suitable thermostatic controls (not shown),maintains the temperature of the cleansing liquid in the tank 50 at asuitable level. Not shown, but which may be included, is a device foradding a cleansing detergent to the liquid in tank 50. During normaloperation, pumps 32 and 48 are continuously driven, usually by separatemotors, once the warewash system 10 is started for a period of time.

The warewash system 10 may optionally include a power rinse (also knownas post-wash) chamber or zone (not shown) that is substantiallyidentical to main wash chamber 40. In such an instance, racks of waresproceed from the wash chamber 40 into the power rinse chamber, withinwhich heated rinse water is sprayed onto the wares from upper and lowermanifolds.

The racks 12 of wares 14 exit the main wash chamber 40 through a curtain52 into a final rinse chamber or zone 54. The final rinse chamber 54 isprovided with upper and lower spray heads 56, 57 that are supplied witha flow of fresh hot water via pipe 62 running from a hot water booster70 under the control of a variable speed pump 114 (or alternatively anyother suitable valve capable of automatic control). A rack detector 64may be actuated when a rack 12 of wares 14 is positioned in the finalrinse chamber 54 and through suitable electrical controls (e.g., thecontroller mentioned below), the detector causes actuation of pump 114which delivers incoming water and causes hot rinse water to move fromthe booster 70 to the spray heads 56, 57. The water then drains from thewares and is directed into the tank 50 by gravity flow. The rinsed rack12 of wares 14 then exits the final rinse chamber 54 through curtain 66,moving into dryer unit 18, before exiting the outlet end 17 of themachine.

An exhaust system 80 for pulling hot moist air from the machine (e.g.,via operation of a blower 81) may be provided. As shown, a cold waterinput 72 line may run through a waste heat recovery unit 82 (e.g., afin-and-tube heat exchanger through which the incoming water flows,though other variations are possible) to recover heat from the exhaustair flowing across and/or through the unit 82. The water line or flowpath 72 then runs through one or more condensers 84 (e.g., in the formof a plate heat exchanger or shell-and-tube heat exchangers, thoughother variations are possible), before delivering the water to thebooster 70 for final heating. A condenser 88 may be located in the washtank and a condenser 90 may be located in the blower dryer unit 18. Asecond waste heat recovery unit 92 may also be provided.

Referring now to FIG. 2, the flow configuration for both incoming freshcold water and for refrigerant are shown. Cold fresh water is firstheated by the hot air passing through the waste heat recovery unit 82,then heated further by refrigerant when passing through condenser 84.The heated water then enters the booster 70 for final heating. Therefrigerant medium circuit 100 includes an electronic thermal expansionvalve 101, which leads to a waste heat recovery unit 92 to recover heatfrom warm waste air (e.g., the exhaust air flow) after some heat hasalready been removed from the exhaust air flow by unit 82. A compressor102 compresses the refrigerant to produce superheated refrigerant, whichthen flows sequentially through the condensers 88, 90 and 84.

Generally, condenser 88 may take the form of coil submerged in the washtank 50 to deliver refrigerant heat to the wash water, condenser 90 maytake the form of a coil over which the drying air blows to deliver somerefrigerant heat to the drying air and condenser 84, which may be aplate-type heat exchanger, delivers residual refrigerant heat to theincoming fresh water. The incoming water to the booster heater passesthrough both the waste heat recovery unit 82 and condenser 84. In theevent of undesired conditions within the machine, adjustments can bemade to compensate.

In this regard, one or more sensors 110 are provided to monitor theconditions of the subcooled refrigerant. The monitoring may becontinuous, periodic or triggered by some event (e.g., identification ofa rack at a certain location in the machine). By way of example, both atemperature sensor and a pressure sensor may be used to monitor thesubcooled refrigerant medium downstream of the last condenser 84 andupstream of the thermal expansion valve 101. If the monitoring indicatesthat the condition of the subcooled refrigerant medium has departed froma set specification, then corrective action can be take.

For example, any of the following conditions within the machine couldlead to the condition of the subcooled refrigerant medium falling belowa desired condition operating range, meaning the refrigerant medium hasnot been condensed sufficiently: an increase in the incoming cold watertemperature, a decrease in the incoming cold water rate, an increase inthe incoming cold water temperature and a decrease in the incoming coldwater rate, an increase in waste moist hot air rate, an increase inwaste moist hot air temperature, both increase in the waste moist hotair rate and waste moist hot air temperature, a decrease in the load onthe warewash machine with an increase in the waste moist hot air rateand/or waste moist hot air temperature, or an inability of one of thecondenser(s) to absorb or transfer the intended heat, as well as anycombination of the above. All of these conditions will cause a decreasein the amount of condensation of the refrigerant medium that takes placein the refrigerant medium circuit 100 and could eventually cause thebelow range condition of the subcooled refrigerant medium.

When a low or below range subcooled condition is identified, any or allof the following corrective actions could be initiated: controlling thecompressor 102 to slow down while the electronic thermal expansion valve101 automatically adjusts to maintain the necessary superheat to thecompressor (e.g., based upon indications from a temperature sensor 115),decreasing the speed of exhaust fan 81 while monitoring air flow viameter 106 to maintain the necessary heat load across the waste heatrecovery units 82 and 92 and to maintain the necessary superheat to thecompressor 102, or increasing the speed of variable speed pump 114 thatdelivers the incoming cool fresh water. Any of these actions willincrease the level of condensation that takes place and can be used tobring the condition of the subcooled refrigerant medium back up into thedesired operating range.

As another example, any of the following conditions within the machinecould lead to the condition of the subcooled refrigerant medium fallingabove a desired condition operating range, meaning the refrigerantmedium has been overly condensed or subcooled: a decrease in theincoming cold water temperature, an increase in the incoming cold waterrate, both decrease in the incoming cold water temperature and increaseof incoming cold water rate, a decrease in waste moist hot air rate, adecrease in waste moist hot air temperature, a decrease in both thewaste moist hot air rate and waste moist hot air temperature, anincrease in the load on the warewash machine with a decrease in thewaste moist hot air rate and/or waste moist hot air temperature. All ofthese conditions will cause an increase in the amount of condensation ofthe refrigerant medium that takes place in the refrigerant mediumcircuit 100 and could eventually cause the above range condition of thesubcooled refrigerant medium.

When a high or above range or overly subcooled condition is identified,any or all of the following corrective actions can be initiated:controlling the compressor 102 to speed up while the electronic thermalexpansion valve 101 adjusts to maintain the necessary superheat to thecompressor, or increasing the speed of the exhaust fan 81 to maintainthe necessary heat load across the waste heat recovery units 82 and 92in order to maintain the necessary superheat to the compressor 102, ordecreasing the speed of the variable speed pump 114 that delivers theincoming cool fresh water. Any of these actions will decrease the levelof condensation that takes place and can be used to bring the conditionof the subcooled refrigerant medium back down into the desired operatingrange.

Moreover, in a situation where the heat load required by one or more ofthe condensers is satisfied, the speed of both the compressor 102 andexhaust fan 81 may be decreased, relying upon the excess heat load tomaintain the minimum heat required in the machine and also to preventunnecessary steam escape from the loading and unloading ends of themachine. In a standby mode of the machine (e.g., when wares are notbeing moved through the machine for cleaning) the speed of the exhaustfan 81 may be decreased to conserve heat in the machine. The exhaust fan81 is typically on when the compressor 102 is on to prevent lowpressure, unless conditions are close to high pressure, in which casethe fan 81 may be shutdown. The moist hot air temperature (as indicatedby temperature sensor 108) and flowrate (as indicated by sensor 106) maybe used to determine the fan speed to maintain a desired set temperaturedrop across the waste heat recovery units 82 and 92, thereby maintainingthe needed superheat and exhaust conditions.

By way of example, the subcooled condition of the refrigerant medium maybe a difference between the actual temperature indicated by thetemperature sensor 110 less a condenser saturation temperaturecorresponding to the pressure indicated by pressure sensor 110. Anexemplary acceptable subcooled condition operating range may be between10° F. and 15° F., though variations are possible. Above 15° F.indicates the refrigerant medium has been overly condensed or subcooled,and below 10° F. indicates that the refrigerant medium has not beencondensed enough (e.g., gas may be present). The condenser saturationtemperature may be determined by reading the pressure indicated bypressure sensor 110 and (i) using a refrigerant pressure/temperaturechart or table (e.g., stored in controller memory) to convert thepressure reading to the condenser saturation temperature or (ii) usingan equation fitted to a refrigerant medium pressure/temperature chart toconvert the pressure reading to the condenser saturation temperature.

A controller 150 may be provided to effect initiation and control of anyof the corrective actions mentioned above based upon indications fromthe temperature sensor and pressure sensor, as well as for controllingother functions and operations of the machine as discussed above. Asused herein, the term controller is intended to broadly encompass anycircuit (e.g., solid state, application specific integrated circuit(ASIC), an electronic circuit, a combinational logic circuit, a fieldprogrammable gate array (FPGA)), processor (e.g., shared, dedicated, orgroup—including hardware or software that executes code) or othercomponent, or a combination of some or all of the above, that carriesout the control functions of the machine or the control functions of anycomponent thereof. The controller may include variable adjustmentfunctionality that enables, for example, the acceptable subcooledcondition operating range to be varied (e.g., via an operator interfaceassociated with the controller 150 or via a restrictedservice/maintenance personnel interface).

Ensuring that the refrigerant medium remains in a desired operatingrange as indicated above can help system operation by (i) assuring thatthe refrigerant medium is fully condensed to assist efficient operationof the thermal expansion valve 101, and/or (ii) reducing or eliminatingthe presence of gas in the refrigerant medium at the upstream side ofthe thermal expansion valve as the presence of such gas will tend torestrict refrigerant medium flow hence starving the evaporator ofrefrigerant medium, and/or (ii) assuring that the refrigerant medium isnot overcooled coming out of the condenser chain, as such overcoolingwill require more energy delivery to the refrigerant medium at theevaporator in order to raise the refrigerant medium to desiredcompressor suction conditions, and if the evaporator is unable todeliver sufficient energy the performance and/or life of the compressormay be adversely impacted.

The above machine provides an advantageous method of correctingundesired conditions of a refrigerant medium circuit in a warewashmachine. In particular, the method involves: identifying anunder-condensed condition of subcooled refrigerant medium in therefrigerant medium circuit or an over-condensed condition of subcooledrefrigerant medium in the refrigeration medium circuit; and in responseto identification of the under-condensed or over-condensed condition,varying at least one of (i) a speed of a compressor of the refrigerantmedium circuit, (ii) a speed of an exhaust fan that causes air flowacross the waste heat recovery unit or (iii) a speed of a pump thatcontrols incoming water flow through the waste heat recovery unit andthe condenser. In one implementation, the identifying step includessensing a refrigerant medium temperature and a refrigerant mediumpressure downstream of all condensers in the refrigerant medium circuit.In one example of such an implementation, the identifying step includesdetermining a difference between the sensed refrigerant mediumtemperature less a condenser saturation temperature corresponding to thesensed refrigerant medium pressure. If the under-condensed condition ofsubcooled refrigerant medium is identified, the varying step involves atleast one of: (i) reducing the speed of the compressor, (ii) reducingthe speed of the exhaust fan or (iii) increasing the speed of the pump.If the over-condensed condition of subcooled refrigerant medium isidentified, the varying step involves at least one of: (i) increasingthe speed of the compressor, (ii) increasing the speed of the exhaustfan or (iii) decreasing the speed of the pump. The method may alsoinvolve monitoring temperature and flow rate of exhaust air andresponsively adjusting the speed of the exhaust fan to maintain a settemperature drop across the waste heat recovery unit.

It is to be clearly understood that the above description is intended byway of illustration and example only and is not intended to be taken byway of limitation, and that changes and modifications are possible.Accordingly, other embodiments are contemplated and modifications andchanges could be made without departing from the scope of thisapplication. For example, the term refrigerant commonly refers to knownacceptable refrigerants, but other thermal fluids could be used inrefrigerant type circuits. The term “refrigerant medium” is intended toencompass all such traditional refrigerants and other thermal fluids.Embodiments with varying numbers of waste heat recovery units and/ornumbers of condensers are also contemplated.

What is claimed is:
 1. A warewash machine for washing wares, comprising:a chamber for receiving wares, the chamber having at least one washzone; a waste heat recovery unit arranged to transfer heat from exhaustair of the machine to incoming water traveling along a water flow paththrough the waste heat recovery unit to a booster heater of the machine;a refrigerant medium circuit including at least a first condenserarranged to deliver refrigerant medium heat to the incoming water; and acontrol arrangement for monitoring subcooled refrigerant mediumcondition and for responsively modifying operation of one or more of:(i) speed of a compressor of the refrigerant medium circuit, (ii) speedof an exhaust fan the causes air flow across the waste heat recoveryunit or (iii) speed of a pump that controls incoming water flow alongthe water flow path.
 2. The machine of claim 1 wherein the controlarrangement includes a refrigerant medium temperature sensor and arefrigerant medium pressure sensor downstream of all condensers in therefrigerant medium circuit.
 3. The machine of claim 2 wherein thecontrol arrangement includes a controller connected with the refrigerantmedium temperature sensor and the refrigerant medium pressure sensor,the controller configured to determine a subcooled condition of therefrigerant medium and to responsively control at least one of: (i) thespeed of the compressor, (ii) the speed of the exhaust fan or (iii) thespeed of the pump.
 4. The machine of claim 3 wherein the subcooledcondition of the refrigerant medium is a difference between an actualtemperature indicated by the refrigerant medium temperature sensor lessa condenser saturation temperature corresponding to a pressure indicatedby the refrigerant medium pressure sensor.
 5. The machine of claim 4wherein the controller is configured to identify a predefined subcooledcondition indicative of under-condensing of the refrigerant medium andto responsively effect at least one of: (i) a reduction in the speed ofthe compressor, (ii) a reduction in the speed of the exhaust fan or(iii) an increase in the speed of the pump.
 6. The machine of claim 4wherein the controller is configured to identify a predefined subcooledcondition indicative of over-condensing of the refrigerant medium and toresponsively effect at least one of: (i) an increase in the speed of thecompressor, (ii) an increase in the speed of the exhaust fan or (iii) adecrease in the speed of the pump.
 7. The machine of claim 1 wherein thecontrol arrangement is further configured to monitor temperature andflow rate of exhaust air and to responsively adjust the speed of theexhaust fan speed to maintain a set temperature drop across the wasteheat recovery unit.
 8. A warewash machine for washing wares, comprising:a chamber for receiving wares, the chamber having at least one washzone; a waste heat recovery unit arranged to transfer heat from exhaustair of the machine to incoming water traveling along a water flow paththrough the waste heat recovery unit into the machine; a refrigerantmedium circuit including a condenser arranged to deliver refrigerantmedium heat to the incoming water; and a control arrangement includingone or more sensors and a controller for determining a condition ofsubcooled refrigerant medium in the refrigeration medium circuit, thecontroller configured to vary, based at least in part upon the conditionof the subcooled refrigerant medium, one or more of: (i) a speed of acompressor of the refrigerant medium circuit, (ii) a speed of an exhaustfan that causes air flow across the waste heat recovery unit or (iii) aspeed of a pump that controls incoming water flow along the water flowpath.
 9. The machine of claim 8 wherein the controller is configured toidentify a predefined under-condensing condition of the refrigerantmedium and to responsively effect at least one of: (i) a reduction inthe speed of the compressor, (ii) a reduction in the speed of theexhaust fan or (iii) an increase in the speed of the pump.
 10. Themachine of claim 8 wherein the controller is configured to identify apredefined over-condensing condition of the refrigerant medium and toresponsively effect at least one of: (i) an increase in the speed of thecompressor, (ii) an increase in the speed of the exhaust fan or (iii) adecrease in the speed of the pump.
 11. In a warewash machine thatincludes a chamber for receiving wares, the chamber having at least onewash zone, a refrigerant medium circuit including at least one condenserthrough which the incoming water to the machine flows, and a waste heatrecovery unit through which incoming water to the machine flows, amethod of adaptively controlling the machine, the method comprising:identifying an under-condensed condition of subcooled refrigerant mediumin the refrigerant medium circuit or an over-condensed condition ofsubcooled refrigerant medium in the refrigeration medium circuit; and inresponse to identification of the under-condensed or over-condensedcondition, varying at least one of (i) a speed of a compressor of therefrigerant medium circuit, (ii) a speed of an exhaust fan the causesair flow across the waste heat recovery unit or (iii) a speed of a pumpthat controls incoming water flow through the waste heat recovery unitand the condenser.
 12. The method of claim 11 wherein the identifyingstep includes sensing a refrigerant medium temperature and a refrigerantmedium pressure downstream of all condensers in the refrigerant mediumcircuit.
 13. The method of claim 12 wherein the identifying stepincludes determining a difference between the sensed refrigerant mediumtemperature less a condenser saturation temperature corresponding to thesensed refrigerant medium pressure.
 14. The method of claim 13 wherein,if the under-condensed condition of subcooled refrigerant medium isidentified, the varying step involves at least one of: (i) reducing thespeed of the compressor, (ii) reducing the speed of the exhaust fan or(iii) increasing the speed of the pump.
 15. The method of claim 13wherein, if the over-condensed condition of subcooled refrigerant mediumis identified, the varying step involves at least one of: (i) increasingthe speed of the compressor, (ii) increasing the speed of the exhaustfan or (iii) decreasing the speed of the pump.
 16. The method of claim11, further including: monitoring temperature and flow rate of exhaustair and responsively adjusting the speed of the exhaust fan to maintaina set temperature drop across the waste heat recovery unit.